Various air fuel ratio detecting devices have been proposed which make use of characteristics of the oxygen concentration cell action and the oxygen ion pumping action of zirconia as disclosed, for example, with Japanese Patent Laid-Open Publication No. 56-130649. However, the accuracy of such conventional air fuel ratio detecting devices is not sufficiently high as to allow such air fuel ratio detecting devices to be used for detecting a stoichiometric air fuel ratio, such as, for example, for a ternary catalyzer, due to the structure thereof.
In addition, in the case of an O.sub.2 sensor used as a conventional type stoichiometric air fuel ratio detecting device, deviations from the stoichiometric air fuel ratio cannot be readily discriminated or determined, and accordingly, the width of the fluctuations in the feedback control of the air fuel ratio is comparatively great, which will cause variations in the output power of the engine or in the number of engine revolutions during idling of the internal combustion engine.
An air fuel ratio detecting device is disclosed within Japanese Patent Application Number 60-262982 which corresponds to U.S. Pat. No. 933,850 wherein a sensor cell detects the difference between the concentration of oxygen within the exhaust gas and the concentration of oxygen within a reference gas so as to develop a corresponding electrical signal. In response to the electrical signal, a controlling means produces and delivers an electrical controlling signal to a pump cell so that the pump cell may cause, in response to the electrical controlling signal received, movement of oxygen ions until the level of the air fuel ratio, and the time at which the stoichiometric air fuel ratio is reached, are detected by first and second detecting means from the information regarding the air fuel ratio as transmitted from the controlling means to the pump cell.
However, where an air fuel ratio detecting device of the aforementioned type is employed, there is the problem that the degree of accuracy of the device may be low due to a possible error between products or due to the fact that the device may deteriorate with time due to extensive use.